Various optical discs serving as information recording media have been proposed. Among the optical discs, optical discs of DVD (Digital Versatile Disc) standard whose recording capacity is about seven times as large as optical discs of CD (Compact Disc) standard have rapidly spread in recent years. DVD-Video discs that contain video signals on DVD discs are mass-producible through duplication, and therefore, are widely used as distribution and rental media in place of VHS (registered trade name) video tapes and the like.
Other optical disc standards such as DVD-RAM, DVD-R, DVD-RW, +R, and +RW standards that allow users to record information signals are also rapidly spreading for media used with personal computers (PCs) and video recorders.
For CD-standard optical discs, there are popular standards such as CD-R that allow users to record information signals on the discs.
Optical disc recorders are required to have a function of recording information signals on DVD-standard optical discs with a light source of 650-nm band, as well as on CD-standard optical discs with a light source of 780-nm band. As mentioned above, there are a variety of standards for DVD-standard optical discs, and there is a need to cope with these standards to write and read the discs. To meet the need, several optical pickup apparatuses have been proposed.
Optical pickup apparatuses capable of recording and reproducing data to and from optical discs of various standards have complicated functions and structures, and therefore, are difficult to manufacture. For such optical pickup apparatuses, in particular, for consumer optical pickup apparatuses, there are increasing requirements of performing multiple functions, simplifying structures, reducing size and weight, minimizing manufacturing processes, and lowering costs.
To meet the requirements, various optical pickup apparatuses that are compact, light weight, and capable of reproducing or recording/reproducing CD- and DVD-standard optical discs have been proposed.
An example of one of such optical pickup apparatuses is shown in FIG. 1. This apparatus has been proposed by the inventor of the present invention. In FIG. 1, the optical pickup apparatus has a first laser source 101 to emit laser light of first wavelength and an optical device 102 that incorporates a second laser source to emit laser light of second wavelength. In FIG. 2, the optical device 102 integrally has the second laser source 103, a hologram element 104, and a light receiving element 105. In FIG. 3, the light receiving element 105 has light receiving parts 106 each divided into a plurality of light receiving regions.
In the optical pickup apparatus, laser light of each wavelength produces three beams, which are emitted to a recording track 201a on an optical disc 201. Reflected beams from the optical disc 201 are diffracted by two divided regions of the hologram element 104 as shown in FIG. 2 and are received by predetermined ones of the light receiving regions of the light receiving element 105. At this time, reflected beams of the first and second wavelengths are received by the same light receiving regions.
In the optical pickup apparatus, the light receiving regions of the light receiving element 105 separately provide light detected outputs from which information signals and error signals related to the optical disc are obtained.